1. Field of the Invention
This invention relates to orthopedics and particularly to control of clamps and other accessories on spinal rods during implantation procedures.
2. Description of the Prior Art
During preparation for implantation of spinal fixation devices, various hooks and clamps are installed on a spinal rod. They are not fixed to the rod, since it is necessary to precisely locate and fix them only after placement in the body. But a spinal rod with an array of fixation devices loosely mounted thereon in preparation for implantation in the human body can be difficult to handle without the devices becoming significantly displaced and disoriented, even to the extent of sliding and falling off the end of the rod. For example, in the TSRH Spinal Implant System marketed by Danek Medical, Inc., the assignee of this application, a series of eyebolts which connect hooks, screws, and plates are positioned along a spinal rod. The connecting elements are used to attach these various hooks and screws to the rod at an infinite number of possible positions. As the surgeon approaches the patient with this plurality of fixation elements strung along the rod, there exists the opportunity for these eyebolt connecting elements to slide off one end of the rod. The ability to temporarily or provisionally position these eyebolts on the rod so that they do not lose their position, would significantly improve the system.
Prior art systems incorporating set screws on their fixation means already exist. Most of which I am aware use the set screws to fix the devices on the rod after they are suitably positioned in the body. They do not lend themselves to simply snugging the device on the rod during handling prior to implantation. Only one spinal fixation system of which I am aware possesses a fixation element which incorporates a means by which it can be temporarily held in position along a spinal fixation rod prior to implantation. It is the Cotrel Dubousset (C/D) instrumentation which uses a blocker which is essentially a cylindrical element with a set screw in it. This cylindrical element is used as the primary means of fixing hooks or screws to the spinal fixation rod. The set screw in the blocker is not only used to provisionally position the cylindrical element but also to provide final tightening of the blocker on the rod. An example is shown in Cotrel U.S. Pat. No. 4,641,636.
The C/D blocker significantly differs from the present invention in that, with the C/D blocker, the same set screw which is used to provisionally tighten the blocker is also used to provide final fixation on the rod. In contrast, various embodiments of the present invention include an eyebolt which uses a 1/4" threaded fastener to provide final fixation. In accord with the present invention, the provisional tightening means does not alter this primary means of fixation between the eyebolt, rod and hooks or screws.
It is an object of the present invention to provide independent means to provisionally position a spinal fixation element on a long spinal fixation rod in order to facilitate final assembly of the implant system in vivo.